The present invention relates generally to wireless communication devices, and more particularly to a system and method for intuitively indicating the signal quality of a wireless communications link.
Most wireless communication devices are mobile stations, such as handheld telephones that are used by pedestrians, or individuals traveling in automobiles. A mobile station can contact another mobile station, or a fixed position relay station, to communicate with other users in the communication system. Typically, a mobile station is free to roam. That is, a mobile station is allowed to operate as it travels through a variety of geographical regions. Often, communication networks are broken up into cells, such as in cellular telephone networks. These cells correspond approximately to geographical regions inside the communication network. As a mobile station, or cellular telephone moves through geographical regions it will change cells, communicating with proximate cells as it moves.
The geographical area in which communications are exchanged with a wireless communications device is typically called a coverage area. The coverage area of a cellular system is limited by a number of parameters. The presence of nearby tall buildings, mountains, or hillsides, shadow (block) radio frequency (RF) signals between a mobile station and a communicating base station. Coverage is also limited by multi-path interference, or the arrival of echoed copies of the same communication at two different periods in time. Operator-configurable system parameters also effect the coverage area. These parameters include the positioning of base station antennas, the selection of which base station communicates with the mobile station, and the transmit power levels of the mobile station and the base station. Co-channel interference between multiple mobile stations and base stations, using the same radio frequency in adjoining cells, also limits the coverage area.
Because of fierce competition between wireless communication providers, and the user's expectation that cellular networks should provide the same level of performance as fixed wireline networks, system operators are active in adjusting system parameters to achieve the optimum performance. In many cases, system parameters are adjusted on a daily basis. Users find that certain so called "dead spots", or locations where communications are frequently dropped or cannot be initiated, remain constant. Other "dead spots" come and go as the side effects of optimizations performed in the network. For example, a cell-site antenna may be re-aimed to provide a stronger signal to one coverage area at the expense of a weaker signal in a second coverage area.
Traditionally, the most qualitative assessment of a fixed line telephone link has been the listener's perception of noise mixed with the intended signal. More recently, analog cellular telephone users have come to rely upon the background static noise as a qualitative assessment of the quality of the communication link. That is, the degree of static that an analog phone user hears tends to be a good indication of whether the call is likely to be dropped, and if the call is dropped, how likely it will be that a new call can be initiated from the same location. The ability to initiate a new call is critical since higher RF signal levels are generally required for initiating a call, as opposed to maintaining an existing call.
Since a majority of the cellular telephones currently in existence are handheld, pedestrian or automobile users play an active role in determining the reliability of their communication link. That is, wireless telephone users often adjust their location to improve the quality of the radio link, thereby reducing the likelihood that the call will be dropped. For this reason, one sees wireless telephone users placing calls near windows or exterior doors where the base station signal is strongest. When calls are dropped, users rely upon their memory of static levels to select the optimum location for initiating a new call.
Presently, second generation cellular telephone systems are being deployed. These systems generally use digital schemes instead of the previously used analog techniques. In addition, digital broadcast television and pager systems are currently in development. Generally, these systems allow operators to support more users with the same limited bandwidth. These digital systems also provide new customer services, resistance to eavesdropping and fraud, and longer battery life. Digital systems also provide a more consistent audio quality. It is believed that in the future, digital systems will replace analog systems.
FIG. 1 illustrates the perceived audio quality of an analog versus digital radio link. In an analog system, the audio quality is highly correlated to the radio link quality. In a digital system, this is not necessarily the case. Digital cellular systems rely upon compression techniques to reduce the transmitted bandwidth requirements. In addition, coded bits are added to the data stream to allow the receiving entity to detect and correct minor errors in the wireless radio communication link. As shown in FIG. 1, when the radio link is good, the received digital cellular speech is perceived as lower in quality than analog speech. This is due to the losses attributable to speech compression. However, as the radio link quality decreases, the ability of the digital system to correct certain errors, results in the maintenance of speech quality at a level which eventually exceeds that of the analog system. At some point, the link becomes so poor that even the digital system's error correction scheme is no longer effective. In practice, such a poor link is shown to be inadequate for maintaining digital, as well as analog communications.
Near "dead spots", a digital telephone may be on the verge of dropping a call, and yet, the user will have little warning that communication is on the verge of interruption. The user of an analog cellular telephone in a similar situation would be warned of a perilous communication link due to the presence of familiar static mixed in with the intended signal. Because the users of digital telephones are unaware of perilous communication links, they are unable to take measures to improve the link. That is, they are unaware that they should change position to improve the communication link. Interspersed muted audio frames are the only sign that some segments of the digital communication have been so poorly received that they are lost. However, in high ambient noise environments, such as typically encountered by a handheld telephone user, it is very difficult to detect these warning signs. In fact, it is only possible to detect these muted frames when the other party is speaking continuously. If the transmitting party is in a quiet setting with no background noise and is not speaking, it is impossible for the digital cellular telephone user to determine if speech frames are being muted.
It would be advantageous if a digital cellular telephone user had a real time indication of the quality of the wireless communications. With such an indicator, telephone users could adjust their location to avoid missing a communication, thereby reducing the chances of having a call dropped.
It would be advantageous if a digital cellular telephone user had an intuitive indicator of the quality of a wireless communications link.
It would also be advantageous if a digital cellular telephone user had a static noise warning to indicate the state of the radio link quality so that they could move positions as analog cellular telephone users do.
It would be advantageous if wireless video receivers had an intuitive, real time, indication of the state of the communication link quality. It would likewise be advantageous if that indicator was a snow-like visual degradation and static sound similar to that of an analog television signal.
Accordingly, in a wireless communication system including a plurality of intercommunicating transceivers to send and receive messages of digitally encoded information, a method of indicating the signal quality of a received message is provided. Alternately, the system includes a plurality of receivers to receive messages of digitally encoded information. The method comprises the steps of: a) estimating the quality of the received message to derive a signal quality estimate and; b) activating an indicator in response to the signal quality estimate in step a), whereby a transceiver user is warned of a poor communications link.
It is an aspect of the invention that the indicator activated in step b) is a static noise sound, whereby the presence of static gives the transceiver user an intuitive sense of the received message signal quality. It is another aspect of the invention to include the further step, following step a), of averaging the estimated signal quality of messages received over a plurality of predetermined first periods of time to create an average signal quality estimate; and activating the indicator in step b) in response to the average signal quality estimate, to present the warning indicator to the user over a predetermined number of predetermined second periods of time. A static noise pattern presented to the user closely simulates the characteristics of an analog receiver.
It is an aspect of the invention that the signal quality estimated in step a) is responsive to the following received message quality data:
1. received message signal strength, which provides a measurement of carrier power of a received message; PA1 2. block decoder status, which indicates whether received messages are successfully decoded into information; and PA1 3. path metric data, which provides a measurement of the corrections required to decode message information. The signal quality is, therefore, based on carrier power, the amount of lost information, and the amount of corrected information. PA1 4. mobile station transmitter carrier power level, which provides an indication of signal quality as measured by a communicating base station; PA1 5. timing advance, which provides a measurement of how far a mobile station is from a communicating base station; and PA1 6. the status of the discontinuous transmission (DTX) function. The message quality standards are adjusted in response to the increased sensitivity of the transceiver to message errors when DTX mode is in use.
In one preferred embodiment, the communication system is a GSM cellular phone network with intercommunicating mobile station telephones, in which the signal quality estimated in step a) is also responsive to the following network-controlled message quality data:
In another preferred embodiment of the invention the communication system is a digital television signal broadcast to digital televisions, and the signal quality estimated in step a) is also responsive to the detection of the loss of sequential broadcast frames. The warning indicator in step b) is a snow-like visual degradation, whereby the user sees an intuitive warning that the received message quality is poor.
A wireless communication system including a plurality of intercommunicating transceivers to send and receive messages of digitally encoded information is also provided. Alternately, the system includes a plurality of receivers to receive messages of digitally encoded information. The system for indicating the signal quality of a received message comprises a signal quality estimator including inputs to accept received message quality data, and an output to provide a signal quality estimate in response to the received quality data. The system also comprises an indicator having an input operatively connected to the output of the signal quality estimator to accept the signal quality estimate, and an output, to warn of poor signal quality, which is activated in response to the signal quality estimate. The indicator warns a user of a poor communications link.